This invention relates to a capacitor discharge type ignition system for an internal combustion engine, and more particularly to an ignition system for an internal combustion engine with an overrunning prevention circuit.
Conventionally, there has been available an ignition system for an internal combustion engine adapted to electrically prevent an overrunning of the engine, in which the generation of an ignition spark at an ignition plug is stopped or suppressed when the rotational speed of the engine exceeds a preset rotation. With this conventional method, however, intermittent occurrence of ignitions is repeated and hence the rotation of the engine repeats periodic increase and decrease. Also, an air-fuel mixture drawn into a combustion chamber enters directly an exhaust system when the ignition discharge is in ceasing and it is ignited by heat generated from a muffler at high temperatures, giving rise to an adverse burst of flame from the muffler exit.
Another conventional method which electrically retards the ignition timing in an ignition circuit to prevent an overrunning is disclosed in U.S. Pat. No. 4,144,859. In such a method, however, the value of retarded angle is limited to a fixed value and when an engine rotation exceeds the fixed value, insufficient protection against the overrunning results.